Digital computer systems are used in a number of applications in which virtually continuous availability of data is important to the operation of businesses or other entities using the systems. Generally, computer centers will periodically produce back-up copies of data on their various digital computer systems. Such back-up copies are usually not maintained on a continuous basis, but instead at particular points in time, often at night when the normal processing load on the computer centers is reduced and modifications to the data being backed up may be minimized, and in any case represent the data at the particular points in time at which the back-up copies are generated. Accordingly, if a failure occurs between back-ups, data which has been received and processed by the digital computer systems since the last back-up copy was produced, may be lost. Typically, such back-up copies will be maintained by the computer centers at their respective sites so that they may be used in the event of a failure, although some off-site archival back-ups may be maintained. Significant additional problems arise in the case of, for example, catastrophic events that can occur, such as may result from, for example, fire, flood or other natural disasters, intentional tampering or sabotage and the like, which may result in unintentional or intentional damage to an entire site or some significant portion thereof, since some or all of the back-up copies may also be damaged and the data contained thereon may be unavailable.
Several backup strategies have been developed. In one strategy, software which maintains and controls the data to be backed up, such as database software, initiates and performs the backup operation. In such an arrangement data, generally in the form of incremental changes to a database, is provided by the database software to a backup management software, which stores the data on a backup device. One advantage of this strategy is that, since only incremental changes are backed up, less data needs to be backed up at any point in time. A disadvantage is, however, that although less data is copied with this strategy, a load is still exerted on the production system processing the database software.
In a second strategy, backups are performed outside the database software. In this strategy, data files are backed up independently of the database software. While this minimizes the load on the production system processing the database software and can result in relatively high-speed backups of full data files, the backup and restore operations do not make use of the facilities that are currently provided in commercial database software.
U.S. patent application Ser. No. 09/052,579 filed on even date herewith in the names of Madhav Mutalik, et al., and entitled "System And Method For Backing Up Data Stored In Mass Storage Subsystem Under Control Of A Backup Server" and U.S. patent application Ser. No. 09/052,318, filed on even date herewith in the names of Madhav Mutalik, et al., and entitled "System And Method For Backing Up Data Stored In Multiple Mirrors On A Mass Storage Subsystem Under Control Of A Backup Server" (both of which are generally identified herein as the Mutalik, et al., applications) describe arrangements for backing up data stored on a mass storage subsystem using a backup server. In response to requests from an application executed by, for example, a host computer, the backup server performs the backup operation, relieving the host computer of that responsibility and allowing the host computer to perform other operations concurrently with the backup operation, thereby enhancing the throughput of the host computer. In one embodiment, the backup server is in the form of a suitably programmed computer, the computer comprising, for example, a workstation or personal computer. A problem arises in connection with such an arrangement, since the file system and file formats and structures provided by the host computer's operating system to manage data files for the host computer and its applications, may differ from those that the operating system used by the backup server's computer.